1. Field
One embodiment of the invention relates to an information processing apparatus such as a personal computer, and a control method of controlling the operation of the apparatus.
2. Description of the Related Art
In recent years, in the technical field of information processing apparatuses such as personal computers, attention has been paid to a third-generation I/O interconnect interface that is called “PCI EXPRESS”. PCI EXPRESS is a standard for interconnecting devices via a communication path that is called “link”. PCI EXPRESS is stipulated by PCI SIG (Peripheral Component Interconnect Special Interest Group). In the PCI EXPRESS standard, transmission of data between devices is executed using packets.
In the PCI EXPRESS standard, a communication path control function, which can set the link at a low power state even if the device is in an active state, is provided. This communication path control function is referred to as “Active State Power Management (ASPM)”. The state of the link is automatically set by hardware from an active state to a low power state (standby state) when the link is in an idle state. When a need for communication arises, the state of the link is restored by hardware to the active state from the standby state. The ASPM function can reduce useless power consumption during the idle state of the link, and can reduce the power consumption of the information processing apparatus.
Jpn. Pat. Appln. KOKAI Publication No. 2004-157590 discloses a technique wherein power consumption is reduced by switching the bus width of a data bus from a 32-bit width to a 16-bit width.
In the technique of KOKAI No. 2004-157590, however, if the bus width is switched to the 16-bit width, the data transfer speed of the bus considerably lowers.
In addition, in the ASPM function, the link is set in the standby state when the link is in the idle state. Thus, unlike the technique of KOKAI No. 2004-157590, the actual data transfer speed is not affected.
However, in order to restore the state of the link from the standby state to the active state, a delay will occur. The delay may cause degradation in system performance. Consequently, if the ASPM function is always used, the real performance of the system cannot fully be exhibited.